Measurement of Tumor T2* Relaxation Times after Iron Oxide Nanoparticle Administration

Our protocol enables standardized tumor T2*measurements across various scanners, manufacturers, and institutions. This protocol enables quality assurance improvement and broad clinical ability without requiring programming language. The main advantage of this technique is the ability to facilitate reliable and consistent tumor T2*measurements across various MRI scanners.

Moreover, it offers an accessible and user-friendly approach, lowering the barriers of adoption. NOIs might struggle with proper sequence setup and ROI selection. The advice is to follow the protocol steps, ensure correct T arrangement and practice ROI drawing for accurate T2*map generation and fitting.

Begin by starting the OsiriX software to install the T2 Fit Map Plugin. Click the Plugins button on the menu bar, then select Plugins Manager from the dropdown menu. Once the Plugin Manager is loaded, select T2 Fit Map from the available plugins.

Click Download Install. Then close the Plugin Manager. Once the software is restarted, load the multi echo gradient deco sequence images as DICOM files into the software.

Change the mouse button function to draw a region of interest or ROI. Then from the dropdown menu, select Oval or Closed Polygon or the desired shape and draw ROIs in the required images with different echo times. Select the ROIs from the images with different echo times for which the T2*map is required.

From the dropdown menu, click the Plugins button, select Image Filters, and then select T2 Fit Map. Once T2 Fit Map is clicked, a dialogue box will open. Then click on Generate Map.

To define the mask ROI on an image series outside the data, open the desired series and select a slice. From the ROI dropdown menu, select Grow Region and the 3D Growing Region radio button. In the Algorithm dropdown menu select Threshold Set the lower and upper thresholds to 0 and X percent of the contralateral muscle signal respectively.

Name the ROI as desired. Then click on the image to place a seed for ROI growing and click Compute. In the ROI menu, select Save All ROIs of this Series.

Next, open the dataset in the 4D viewer. After ensuring that the ROIs are in the first 3D volume, from the ROI menu, select Import ROI(s)Apply mask to map the data by selecting Set Pixel Values To.Then select Apply to ROIs with same name. Check the Propagate to 4D series box, set pixels that are Inside ROIs and set To this new value as zero.

This study shows quantification of T2*relaxation time in a patient with metastatic osteosarcoma. A fitting curve is generated with minimum, mean, and maximum T2*values for the selected ROIs with various echo times for this patient. The color-encoded T2*maps were merged with a contrast-enhanced T1-weighted gradient deco image for anatomical orientation.

It is important to arrange the input multi echo gradient deco images according to their acquisition times. This can be achieved by sorting the imaging data series by acquisition time in the external software under preferences database dropdown menu. Our protocol has significantly enhanced repeatability and reproducibility, providing consistent T2*relaxation times across diverse cancer studies.